1. Field of the Invention
The present invention relates to a liquid droplet discharging head and an ink jet recording device.
2. Description of the Related Art
Generally, an ink jet head is used as a liquid droplet discharging head mounted on an ink jet recording device used in an image recording apparatus, such as a printer, a facsimile machine, a copying machine, or a plotter. As such an ink jet head, an electrostatic ink jet head that discharges ink droplets through a nozzle by deforming and displacing a diaphragm with static electricity is well known. Such a conventional electrostatic ink jet head comprises the nozzle through which ink droplets are discharged, a discharging chamber (also referred to as an ink fluid passage, an ink chamber, a pressure chamber, a pressurizing chamber, or a pressuring liquid chamber) that communicates with the nozzle, a diaphragm that also serves as a first electrode which constitutes a wall surface of the discharging chamber, and a second electrode that faces the diaphragm.
Japanese Laid-Open Patent Application Nos. 6-071882 and 5-050601 disclose conventional electrostatic ink jet heads. In those electrostatic ink jet heads, a silicon substrate is used as a substrate for forming a discharging chamber and a diaphragm, and boro-silicate glass (Pyrex glass) or a silicon substrate is used as a substrate on which an electrode is disposed.
In such an ink jet head, crosstalk may occur when one discharging chamber is energized and the ink therein is pressurized, thus the ink pressure propagates to the ink in the adjacent discharging chambers, resulting in uncontrolled ink discharge. When crosstalk occurs, the quality of images obtained by the ink jet head deteriorates. Especially, crosstalk occurs more frequently, as the nozzle intervals are becoming narrower with higher density arrangement of the nozzles.
To prevent the crosstalk, Japanese Laid-Open Patent Application No. 8-029056 discloses a technique to change the rigidity of the diaphragm by gradually changing the thickness of the diaphragm. Japanese Laid-Open Patent Application No. 7-246706 discloses a technique to increase the rigidity of the discharging chamber by arranging ribs on the wall. Further, Japanese Laid-Open Patent Application No. 11-000993 discloses a technique in which the height of the liquid chamber is limited.
With the electrostatic ink jet head, there is a problem, besides the crosstalk problem, that accuracy needs to be maintained in the bonding of a substrate having the diaphragm to a substrate having the electrode, and in the minute gap between the diaphragm and the electrode.
A conventional ink jet head normally has a discharging density of approximately 128 dpi. As the recording density is increased to 1200 dpi by increasing the number of the scanning paths while using such a head, the recording rate is reduced with the larger number of scanning paths due to low discharging density of the head.
To produce an ink jet head having a discharging density of 300 dpi or higher, the pitch between adjacent bits has to be set to approximately 85 xcexcm. Since the width of the diaphragm for discharging needs to be approximately 60 xcexcm, the partition wall between the bits has to be approximately 25 xcexcm. Depending on the performance of actuators, a wider diaphragm is required. If excellent discharging characteristics are desired, the width of the partition walls has to be reduced. In such an ink jet head, the electrode for driving the diaphragm faces the diaphragm, resulting in even narrower pitch between adjacent bits. With such an ink jet head, there is a problem of poor substrate bonding, besides the crosstalk problem.
In the above high-density ink jet head, it is very difficult to vary the thickness of the diaphragm so as to reduce the crosstalk, or form ribs on the partition wall. The technique of limiting the height of the liquid chamber is not a very practical method, because it is necessary to change the height of the liquid chamber depending on the pitch of the nozzles.
To solve the above problems, the inventors have made intensive studies on an ink jet head that can ensure reliability in bonding of the substrate having the diaphragm to the substrate having the electrode, and can reduce crosstalk.
It is a general object of the present invention to provide liquid droplet discharging heads and ink jet recording devices in which the above-mentioned problems are eliminated.
A more specific object of the present invention is to provide a high-density liquid droplet discharging head that can reduce crosstalk and attain reliability in bonding, and an ink jet recording device that can perform a high-quality recording operation with the high-density liquid droplet discharging head.
The above objects of the present invention are achieved by a liquid droplet discharging head in which the width of the bonding portion between a diaphragm substrate and an electrode substrate is in a range of 5 xcexcm to 25 xcexcm.
In a case where the diaphragm substrate and the electrode substrate are both silicon substrates in this liquid droplet discharging head, the two substrates can be bonded directly to each other. In a case where the diaphragm substrate is a silicon substrate, and the electrode substrate is a glass substrate, the two substrates can be bonded to each other by anode bonding. The width of each partition wall between the discharging chambers should preferably be narrower than the width of each partition wall between the electrodes.
Also, it is preferred that the electrodes are not in parallel with the diaphragm in the width direction of the diaphragm. Further, the discharging density should preferably be 300 dpi or higher.
The above objects of the present invention are also achieved by an ink jet recording device on which the liquid droplet discharging head of the present invention is mounted.
Other objects and further features of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings.